The natural cosmetics market is undergoing rapid change and expansion. Natural cosmetics place priority on natural resources, promote the use of ingredients derived from organic farming, preserve the environment and reduce packaging. Labels defining natural cosmetics have been developed including the Ecocert certification body in France and BDIH in Germany. In particular, to be considered a natural cosmetic, the composition must not contain unauthorized or prohibited starting materials and must comply with a series of specifications.
In this context, formulators are setting out to develop formulations having the same sensory characteristics and effectiveness as the so-called conventional formulations while having access to a much more limited number of ingredients.
One of the main problems encountered relates to the consistency of the developed formulations. In fact, many existing conventional thickeners can produce a wide range of viscosities and textures. These conventional thickeners include in particular the aqueous phase thickeners such as carbopols (carbocypolymethylene), taurate copolymers and acrylamides (non-limiting list), which give high viscosities using low thickener concentrations. The developed formulations are thus viscous and not runny. Conventional thickeners of the type such as silicone or acrylate are not authorized for use in natural cosmetics.
Natural aqueous phase thickeners are not as numerous and generally belong to the gum family: guar gum, carob gum, konjac gum, xanthan gum, sclerotium gum, acacia gum, cellulose gum (modified or not). From a chemical standpoint, they are polysaccharides obtained either by extraction from the plant (guar, carob, konjac, acacia, etc.), or by biotechnological synthesis followed by extraction (xanthan and sclerotium). Polysaccharides are macromolecules composed of chains of sugar monomer units. A macromolecule is composed of several hundred, or even several thousand, sugar residues. They differ in terms of their chemical nature.
In cosmetics, the most interesting texturizers are those which thicken and/or stabilize formulations. The thickening function occurs when the large size of the molecules “clutters” the medium, causing the molecules to get tangled up and hindering the movement of water. The gelling function occurs when the junctions between molecules create a three-dimensional space which traps water. Stabilization occurs when thickening or gelling prevents separation of the phases.
Xanthan gum is obtained by the fermentation of a hydrocarbon substrate by the Xanthomonas campestris bacterium. Xanthan gum is commonly used in pharmaceuticals, cosmetics and foods (additive E415) and is the object of many patents, in particular JP 2008201806 and US 2008131469 (A1). Xanthan gum is a polysaccharide with a very high molecular weight. The backbone is formed of D-glucose units to which side chains are attached, one side chain for two glucose residues. The side chain is formed of three sugars: α-D mannose, β-glucuronic acid and a terminal α-D mannose. Xanthan gum is known to be compatible with other hydrocolloids and in particular to form gels by synergy with galactomannans (derived for example from guar or carob). The gels have little interest in cosmetics because they often have a poor skin feel when used by the final consumer.
In the same manner, sclerotium gum is obtained by a fermentation process of the filamentous fungus Sclerotium rolfssii on a glucose-based medium. Some uses of sclerotium gum in cosmetics have previously been described in patent applications, in particular WO 2004028501 (A1) and JP 2004075596 (A). It is a very high molecular weight homopolysaccharide which gives only glucose residues on hydrolysis. The backbone is formed of β-D glucose residues connected by β (1-3) glycosidic bonds with one β (1-6)-D-glucose side chain every three glucose residues, which prevents chain aggregation.
These two products are widely used, alone or in combination, to develop both natural and conventional cosmetic formulations. They allow the production of stable, thickened solutions over a wide pH range and compatible with electrolytes. However, the concentrations of thickeners needed to obtain viscosities high enough to describe the resulting products as creams result in a runny, tacky feel which is unpleasant for the consumer. Furthermore, the suspending properties of these thickeners do not allow sufficient stabilization of an oil phase to describe the final product as a gel-cream.
Moreover, natural formulations contain many natural emollients or of natural origin such as vegetable oils (sweet almond, sunflower, grape, apricot, etc.) or vegetable butters (shea, mango, cocoa, coconut, cupuacu, illipe, etc.) which penetrate slowly after application, a characteristic which formulators consider undesirable. Solutions of xanthan and/or sclerotium gum have good spreadability but penetrate slowly and leave a greasy feel at the skin surface.
Formulators are therefore at a loss to develop natural gel-creams with a pleasant, non-greasy feel.
Pullulan is a polysaccharide obtained by biotechnology (Aureobasidium pullulans) from starch. It is used to form edible films (food additive E1204). The backbone is a linear a-glucan chain formed of three glucose residues linked α-(1-4) in maltotriose units which are connected to each other by α-(1-6) glycosidic bonds. The structure can contain up to 10% maltotetraose and α-(1-3) branch linkages. Depending on the methods of biosynthesis and purification, pullulan can contain heteropolysaccharides and acid polysaccharides as impurities. In aqueous solution it has low viscosity (hence it cannot be described as a thickener); a 2% aqueous solution of pullulan has an apparent viscosity of approximately 2-3.5 mPa·s. Its adhesive properties together with its good water solubility are what allow its use for developing breath freshener films. On the other hand, these properties are of little interest in cosmetics because tackiness is a negative feature that formulators try to eliminate from their formulations. In addition, the absence of thickening properties makes it of no use to adjust viscosity. Finally, its film-forming ability tends to result in the formation of “fluff” when applied. Nonetheless the film-forming properties of pullulan have been used in cosmetics to form visible films at the skin surface (WO 03026583 (A3)).
Fructan is a polysaccharide obtained by biotechnology whose properties of adhesion and in aqueous solution are very similar to those of pullulan. However, its chemical composition is different: it is a chain of β-(2-6) fructose units with β-(2-1) branches. Like pullulan, it is not a thickener and it forms tacky films.